How do they know?

[LordHaveMurci]

Our new(ish) 12mth old rescue spaniel met his 1st fox last night (with us anyway) & he took off after it.

The puzzling thing is, he pretty much ignores other dogs when he's out, being a working breed he has more interesting things to do than play, my previous cocker was the same.

It can't be scent, pretty sure we were upwind of the fox, it must be like when a cat runs & they chase it, instinctive?

Thankfully all the training paid off & the dog didn't go far

[monoloco]

My German Pointer is the same. If he sees another dog or any size or breed he wants to go and play but if he sees a fox in the field opposite our house he's pumped up, hackles up and itching to get at it.

[AdiT]

Don't know but my Weim' is the same. If he spots one it's an instant response. The last one, he dived up to his chest into a culvert after and came out with white fur in his front teeth from the tip of it's tail. If he picks up the scent his whole body language alters and can't be mistaken for anything else.